In LTE D2D study, it was decided that the D2D signals occupy part of uplink cellular resources (i.e., uplink carriers for FDD and uplink subframes for TDD), as shown in FIG. 2 for the case of FDD. In particular, the D2D signals will occupy some periodical uplink subframes. In order to support the normal downlink cellular transmissions, the uplink cellular control signals (i.e., PUCCH) still have to be transmitted. That is to say in the D2D subframes the cellular PUCCH signals have to be multiplexed with D2D signals through FDM, as shown in FIG. 2. On the other hand, according to the in-band emission interference modeling as described in 3GPP TR38.843 V12.0.1, “Study on LTE Device to Device Proximity Services—radio aspects”, the cellular PUCCH signals suffer from the in-band interference from the D2D signals. FIG. 1 shows an example of in-band emission interference model.
Since the uplink PUCCH signals (e.g., ACK/NACK, CQI feedback etc. depending on the PUCCH format) play an important role in supporting the downlink data transmission, the in-band emission interference from D2D signals to the cellular control signals has to be solved. This invention aims to address this technical problem.
FIG. 1 illustrates an example of in-band interference, based on the modeling method described in 3GPP TR38.843 V12.0.1, “Study on LTE Device to Device Proximity Services—radio aspects” with updated parameters {W,X,Y,Z}={3,6,3,3}.
Up to now, the best existing solution of this problem is through usage of power control for the D2D signal. Such a technical solution is disclosed by the application with the application number 201410041266.0 titled “method of controlling transmission power” and the application with the application number 201410192499.0 titled “method of reducing Impact of D2D In-Band Interference on Cellular Transmission”.
In the first patent application, namely for the power control method, the solution works well in controlling the in-band emission interference to uplink cellular signals. However, it has some disadvantages. The main disadvantage is that by using power control, the D2D signal transmission powers are not uniform for different D2D users (the closer to base station, is the lower the D2D signal transmission power is), thus the D2D transmission range is not uniform. This is not a desirable property for D2D transmissions.
For the restricted resource selection method proposed in the second patent application, the configured D2D subframes are divided into two groups, each group constitutes a number of contiguous subframes, as per the configuration of base station. The D2D users near the base station can only select D2D resources for transmission from one group (say group 1) while the D2D users far from the base station can only select D2D transmission resource from another group (say group 2), such that the in-band interference from the D2D users to the base station is mainly limited to the D2D resource group 1. The main disadvantages of this method are that although the in-band interference to the D2D resource group 2 is largely alleviated, the in-band interference over the D2D resource group 1 is further degraded such that the base station may hardly decode the received PUCCHs over the subframes of D2D resource group 1. Since the uplink PUCCHs may convey the information of ACK/NACK, CQI feedback, and so on, the collapse of the PUCCH detection will lead to loss in downlink throughput.